I agree OP, as someone who does fencing IRL heavy armour should be reducing all damage to the point where you should not be taking any damage. Heavy armour can even absorb the full swing of a halberd, mace and long sword. Only axes / bear form and explosive magics should be able to damage heavy armour.
The drawback to heavy armour should be that your forced to repair it after every fight and that it should be expensive to do so, that way the player must decide if they want to accumulate gold or being protected.
...this is exactly what heavy armor is doing?? It gives you higher AC, making it more likely for the enemy to miss and deal zero damage
because the enemy hits a completely protected part of your body. But you can still be hit - joints in the armor, neck and head if you're not wearing a helmet. Also, AC with the "full hit or complete miss" (and HP for that matter) are abstractions in D&D that simplify complex interactions, and D&D 5e in particular is designed taking this into account. If you changed all armors so they subtracted X from incoming damage, then you'd have to rebalance a bunch of mechanics: concentration, abilities that activate when you take damage, etc.
I don't disagree that different damage types should affect different armors - and monsters - differently. Weapon damage type importantness is something I'd like to see return, especially in a video game which can more easily handle the nitty gritty details.
-1 for any type of weapon/armor durability system in BG3. Just no.